When socks are worn while walking, for example, slipping can occur between the sole of the foot and the inner surface of the sock, or between the outer surface of the sock and the insole of the shoe, depending on the type of yarn used in the sock. This can make walking difficult. Moreover, when socks are worn while playing various sports, and slipping occurs between the inside and the outside of the socks, there is insufficient gripping force when the foot kicks off the ground to generate thrust.
Heretofore, there has been disclosed a sock which has an anti-slip area formed at a position adjacent to the heel portion or sole side of the toe tip portion of the sock (e.g., FIG. 2 of Patent Reference 1).
Heretofore, there has also been disclosed a sock which imparts an anti-slip function to the entire toe tip portion and heel portion by knitting up the toe tip portion and the heel portion using a yarn with a high coefficient of friction (e.g., FIG. 1 of Patent Reference 2).
If the motion of walking is separated into the actions of 1) touching the ground with the heel, 2) transferring the weight to the toes, and 3) kicking off the ground from the base of the toes using the large toe, it is the kicking off action of 3) which most affects the intensity of the force which grips the ground to generate thrust.
During the kicking off action of 3), the toes operate independently to naturally spread in the lateral direction, which produces a strong gripping force to obtain a wider contact surface area with the ground.
Thus, if the frictional force can be increased in only certain areas of the sock which correspond to the base of the toes and to the large toe in the toe area on the sole side of the sock, then the gripping force during the kicking off action can be most effectively increased, without interfering with the lateral spreading of the toes.
In the case of socks worn in ball sports, there are instances where the gripping force needs to be high in certain places on the little toe side in the toe area on the sole side of either the right or left sock, or the gripping force needs to be high on both the large toe side and the little toe side, depending on the player's position.
In any of the above cases, it is important to increase the frictional force of only specified portions of the toe area on the sole side. If frictional force is increased in the entire toe area, then this will naturally result in interference with the lateral spreading of the toes.
However, in the above described prior art sock, as, for example, the sock disclosed in Patent Reference 1, there was the problem that it was impossible to increase the gripping force of portions corresponding to the large toe, for example, because an anti-slip area was provided at a position adjacent to the sole side other than the toe area, rather than providing an anti-slip area within the toe area on the sole side. For the same reason, it was also impossible to increase the gripping force on the little toe side, and it was also impossible to increase the gripping force on both the large toe side and the little toe side.
The technology disclosed in Patent Reference 1 was able to provide an anti-slip area using reciprocating rotation knitting in the foot portion knitted with normal cylinder rotation of a circular knitting machine. However, if an attempt was made to provide an anti-slip area by employing reciprocating rotation knitting in the toe area, there was the problem that the basic shape of the toe area of the sock could no longer be maintained.
There was also the problem that it was impossible to provide a functional area by performing reciprocating rotation knitting in the toe area, even when using functional yarns not only of a type with high frictional resistance, but also functional yarns with high durability and high water absorption properties. In other words, the problems of the prior art were not due to the type of functional yarns used, but rather, because it was impossible to place functional areas in parts of the toe area on the sole side of the sock.
There was the additional problem that the anti-slip effect was insufficient, because no consideration was given to increasing the frictional force between the sole of the foot and the inner side surface of the sock.
The sock of Patent Reference 2 had the problem that there was less freedom for the toes to spread during the kicking off action because the anti-slip effect is provided to the entire toe area. Thus, in this prior art technology, there was the risk of impeding the motion of walking, because the anti-slip effect extended to areas where it was not needed.    Patent Reference 1: Japanese Laid-Open Patent Application No. 2008-75236    Patent Reference 2: Japanese Laid-Open Patent Application No. 2007-162149
The problem to be solved by the present invention is that in the prior art sock, it was impossible to provide a functional area only in a specified area within the toe area on the sole side of the sock.